Electronic piano



May 14, 1940. B. F. MIESSNER ELECTRONIC PIANO Filed Jan 29, 1958 5Sheets-Sheet l 6 lNVENTOR:-

May 14, 1940. B. F. MIESSNER ELECTRONIC PIANO Filed Jan. '29, 1938 3Sheets-Sheet 2 I. l I

May 14, 1940. a. F. MIESSNER ELECTRONIC PIANO Filgd Jan. 29, 1958 3Sheets-Sheet 5 Patented May 14, 1940 UNITED STATES PATENT OFFICEELECTRONIC PIANO Benjamin F. Miessner, Millburn Township, Essex County,N. J., assignor to Miessner Inventions, Inc., Millburn Township, EssexCounty, N. 1., a corporation of New Jersey Application January 29, 1938,Serial No. 187,646

. 2'1 Claims. (01. 84-114) fier and then in turn translated(electro-acousti-- cally) into output tones.

It is anobject of the invention to enhance the l pianistic quality of,or approximation of conventional piano performance by, the output tonesof an electronic piano.

It is an object to provide improved mechanicaelectric translatingapparatus, and arrangements 15 thereof relative to other components,whereby It is another object to provide improved simple and readilyadjustable translating electrodes and relationships thereof to thestrings.

It is another object to provide improved and 35 simplified means forminimizing non-musical components attendant upon tone initiation,particularly in the high treble notes and without sacrifice'of electrodeadjustability.

It is another object to provide novel electrical 40 means forminimizingsuch undesirable components as abovementioned.

It is another object to provide improved and.

simplified means for increasing the rate of damping of the output tonesof the electric piano.

45 It is another object to provide improved and simplified means fordecreasing the direct acoustic sound output of the electronic piano. Itis another object to reduce feed-back from the loudspeaker to thestrings.

It is another object effectively to control the apparent damping of theoutputtones.

It is another object to control this apparent damping while maintainingsubstantially "constant the volume level of the output tones. 55 It isanother object to provide effective, simplified and durable volumecontrol means for the electronic piano.

It is another object to provide a coupling circuit, between thetranslating electrodes and the amplifier input, substantially free ofthe deficiencies of electrical leakage and mechanicalvibration.

It is another object to provide particularly effective and simpleelectrostatic shielding of sensitive portions of the piano. I

-It is another object to provide improved and particularly, eifectivearrangements of electroacoustic translating devices in the electronicpiano. v

'It is another object eflectively to minimizeor suppress regenerative oroscillation-sustaining effects of a feed-back from the. electro-acoustictranslating device to the strings of the electronic piano.

Other and allied objects will more fully'appear from the followingdescription and the appended claims.

In the description of my invention, hereinafter set forth, reference isbad to the accompanying drawings, of which- Figure 1 is a frontelevational view' of an electronic piano according to my invention,with'the' front cover member and most of the action removed;

Figure 2 is a rear elevational view of the instrument of Figure 1, withthe back cover removed;

Figure3 is a substantially vertical cross-sectional view of most of theinstrument, taken approximately along the line H of Figure 1, Figure 3further including a schematic showing of electrical portions 'of theinstrument;

Figure 4 is a fractional substantially vertical cross-sectional viewillustrating a modification in respect of the bridge means of theinstrument;

Figure 5 is a fractional substantially vertical cross-sectional viewillustrating a further modification in respect of the bridge means;

Figure 6 is an enlarged vertical cross-sectional view of the principalcomponents of the hammer action, together with a schematic illustrationof certain electrical control means interrelated with the action-controlmeans;

' Figure 7 is a partial, inclined cross-sectional view of the bridge andelectrode means for the upper treble strings, taken approximately alongthe line of Figure 1, together with a schematic illustration of certainelectrical circuits which may beneficially be associated with thoseelectrode means;

Figure 8 is a vertical cross-sectional view of one of the pedals, takenalong the line 8-8 of Figure 1, together with a schematic illustrationof electrical components associated with that pedal;

and.

Figure 9 is a rear elevational view of the vertical front cover member Hwhen removed from the instrument.

Reference may be had to Figures 1, 2 and 3 for an understanding of thegeneral mechanical construction of the electronic piano with which Ihave illustrated my invention. Herein will be seen a vertical,rectangular metallic plate or frame I serving as the basis to which allother components are directly or indirectly assembled; this plate isconveniently provided around its periphery with the forwardly extendingflange 2. The central portions of the plate 'are apertured; but theplate is reinforced by cross-webs such as 3, some of these being in turnreinforced with forwardly extending flanges such as 4. To the back ofthe plate may be secured a peripheral framework, comprising for examplethe wrestplank 5 across the top, the. wooden cross-member 6 across thebottom, and the vertical wooden end member 1. To the plate I, throughthe medium of this framework, may be supported a vibratile systemcomprising certain bridges (hereinafter described) and a plurality ofvibratile ribs 8the tops of the ribs being secured in the wrest-plank 5,the bottoms of the ribs being secured in the bottom cross-member 6, andthe ribs being preferably slightly bowed forwardly in their centralportions. Forwardly and backwardly extending vertical standards 9 may besecured to the two ends of the plate 9 to form a support therefor and,if desired, to form the exposed ends of the instrument. A bottom frontcross-member may extend between the end standards 9, as may likewise afloor-member Illa, between the cross-member l0 and the plate I. Theremay also be provided between the end standards 9, extending upwardlyfrom the front cross-member III, a removable front cover member H (seeFigure 3). The illustration of ribs 8 has been omitted from Figure 1 inthe interest of clarity of showing.

The top portion of the plate I is suitably apertured to permit aplurality of tuning pins l2 to extend forwardly therethrough fromwrestplank 5, wherein they are secured. From these pins to respectivehitch pins I3 in lower portions of the plate I extend the several tunedstrings of the instrument, of which the upper treble strings areindicated as IS, the lower treble strings as 15, and the bass strings asI4-it-being understood that each of these groups of strings has beenonly fractionally shown in the interest of simplification of thedrawings. strings have been shown as passing from the tuning pins I!under a pressure bar I! and over a ledge l8 defining the upperextremities of their active portions; the bass strings M, which may beoverstrung (i. e., disposed slightly in front of and somewhattransversely to the treble strings), may pass aroundrespective'localizing pins IS in the defining ledge l8. The bridges overwhich the strings pass, and which define the lower extremities of theactive string portions, are hereinafter described.

For impulse excitation of the strings there may be employed a hammeraction, for example of the dropped" type; this, while appearingfractionally in Figure 1 as A, has been indicated in enlarged detail inFigure 6. Briefly, it may comprise keys 20; upper levers 2| adapted tobe raised All the treble.

by the rear ends of the respective keys upon key depression; lowerlevers 22 coupled to the respective upper levers; pivoted hammers 23responsive, through the respective levers and action mechanism notnecessary to detail, to the respective keys to strike the respectivestrings; and normally string-contacting pivoted dampers 26 responsive tothe respective keys to move away from the respective strings. .Atransverse rod 21 may be provided in front of the heels 26a of all thedampers, and may be moved rearwardly at will (as by depression of theconventional sustaining pedal 28, Figure 1) to move all the dampers 26simultaneously away from the strings. A transverse rail 24 may beprovided in front of all the hammer shanks 23a, being supported by rodssuch as 240 pivoted at fixed points such as 24b, and may be movedrearwardly and upwardly at will (as by depression of the pedal 25,Figure 1, acting through lever 25a and rod 251)) to reduce the normalseparation of the hammers from the stringsand hence to reduce the lengthof the hammer stroke, and in turn the strength of the excitation of thestrings by key depression.

For translating the string vibrations into sound there is employed amechanico-electric-acoustic translating system, wherein themechanico-elec- 'tric translation is effected electrostatically. Thussuitable electrode means, hereinafter more particularly described, areprovided adjacent the strings to form therewith minute capacities whichwill'be oscillatorily varied by the string vibrations; these capacitiesare polarized or charged with a relatively high voltage through a highresistance, preferably connected to the electrode means. In Figure 3 acharging voltage source is schematically indicated as 30, having oneterminal connected to the electrode means through the high resistance3|; the other terminal of the source 30 may be connected with plate Iand therethrough with all the strings, their joint potential beingconveniently considered as ground potential. The electrode means areconnected to electronic amplifying means, as through an input orblocking condenser 32 and an input grid leak resistance 33, for theimpression on the amplifier 'of the minute oscillatory voltage changesabovementioned. The amplifier has been schematically indicated forconvenience as comprising the tandemed portions 34, 36 and 38, withcontrol means 35w-35b and 37 interposed between the portions. The outputof the amplifier may be connected to electro-acoustic translating means;these I have schematically indicated in Figure 3 as the speaker 39having for example a response at all audio frequencies but beingparticularly efficient in the lower frequency range, and the speaker 40having for example an efficient response at the high frequencies only.

The general construction thus far outlined will be understood to be nowknown, and not in itself to comprise the instant invention.

According to the preferred embodiment of the instant invention I arrangethe electrode or pick-up means for a group of strings in a bridgeassembly which is integral with the stringsupporting bridge for thosestrings. In Figures 1, 2 and 3 the bridge which supports the treblestrings is shown as ll, the strings passing over it with a bearingthereon and being secured to it as to vibrational movement by engagementwith the conventional bridge pins therein. The bridge 4| is secured tothe several ribs 8 in an appropriate curve transverse to the ribs; thissecuring, as by gluing, may desirably be not merely to the front surfaceof the ribs, but to the rib sides as well-by virtue of the illustratedthickening of the bridge between the ribs.- The bridge. 4| is providedwith a portion 42 of reduced thickness extending underneath the activestring portions (i. e., upwardly) and by this portion the electrodemeans for the treble strings are carried.

Q and to the charging resistance 3| and input condenser alreadymentioned.

I have found the presently described bridge construction to yield a.particularly pianistic output tone-apparently because of especiallyefficiency in the translation of the longitudinal vibrational eil'ect ofthe strings This effect is a vibratory pull by the string on the bridge,bicyclic and otherwise of second-power with respect to each of thevarious partial components of the normal string vibration; this pull inturn rocks the bridge vibratorily, roughly about a line transverselythrough the ribs opposite (i. e., behind) the region of the securing ofthe strings to the bridge. This second-power rocking movement of thebridge, occurring at the bridge pins in the longitudinal direction ofthe strings, causes the extending bridgeportions 42 and u to executerespectively corresponding rocking motions toward and away from thestrings- -and hence produces a corresponding second-power varicadenceand in increasing the initial steepness of that decadence. While in U.S. Patent No. 1,912,293 to me I disclosed electrode means secured to theside of a string-supporting bridge, and in another embodiment to thebridge-supporting ribs near the bridge, sothat this secondpower actionoccurred to an appreciable extent,

. I have nevertheless found the present integral bridge construction,with the electrodemeans- I intimately secured in the bridge,

to been appreciably improved one.

It is essential that the insulation resistance between the electrodemeans and the strings be of a very high order; hard-wood bridgematerials as customarily employed have V in themselves proven deficientin providing this insulation reslstance in structures such as I havedescribed above. 'I have found, however, that if the bridge bethoroughly treated with oil (castor oil, for,

example) so that at least a surface layer portion thereof contains asubstantial percentage of oil, a satisfactory value of insulationresistance may usually be attained. As an expedient alternative oradditional to the-oiltreatment, however, each of the electrode screws 45maybe surrounded within the bridge by bushings 41 of high-gradeinsulating material, such as the phenol-resin com- The several positionsavailable under the trade-name of Bakelitethe, bushings preferablyextending slightly from both front and back surfaces of the bridge.Still another expedient, alternative or additional to the above, forincreasing the insulation resistance is the longitudinal slotting of thebridge between the bridge pins and the electrode means; this has beenillustrated in connection with the treble bridge 4| in Figure 3, the twolongitudinal slots 48 appearing in the mentioned location. .While eachof these expedients is a distinct benefit, I have not ordinarilyiound itnecessary to resort to all coincidentally; for

service under unusually trying atmospheric conditions, however, they mayall be included.

The oil-treatment and/or slotting are useful with other arrangements ofelectrode means on the bridge. Thus in Figure 4 I show a bridge 43'intended for optional substitution for one of the bridges of earlierfigures-for example, for the bass bridge 43, in connection with whichthe importance of adjustability of the electrode means is at a minimum.This bridge 43' is provided with the extending portion 44 correspondingto the portion .44 above described; the electrode means carried by thebridge, however, are in the form of a fixed strip 48 held in spacedrelationship to the bass strings l4 byan intimate securing to thesurface of an insulating strip 50, which in turn is intimately securedto the surface of the extending bridge portion 44'. The bridge of Figure4 may be either oil-treated or provided with one or more slots 48' asshown, with benefits as above described.

While I prefer the integral formation of the bridge for both strings andelectrode means, the

advantage of that arrangement may be retained to an appreciable extentwith separate bridges if at least thestring bridge and preferably bothbridges are formed to fit around, and are secured to, the sides as wellas the front surface of each rib 8 (i. e., to three faces of each rib,as described above as preferred even for the integral bridge)this'preserves a high degree of coupling,

between the bridges as to the rocking movement.

The alternative arrangement of such separate invention at least thetreble strings are arranged in pairs, the two strings of each pair beingsubstantially parallel and similarly tuned to a respective note, andbeing simultaneously excited and damped; and a singleelectrode screw isassociated with each pair, the'axis of the screw being substantiallycentered between, and normal to the plane of, the two strings. For thebass strings I4 and the lower treble strings IS the electrode screws 45may be flat-headed; but for the upper treble strings I6 I prefer toemploy screws with conical heads and, further, to make the apex anglesof those heads progressively more pointed for progressively highernotes. This I have illustrated in the cross-sectional Figure '7, whereinappear the strings ii for several mutually spaced higher treble notes; aflat-headed electrode screw 45 for the lowest-shown stringpair(connected by conductor 46 to the electrodes for the lower treble andbase strings) a slightly, conical-headed screw 45a for a somewhathigher-- note string-pair; and so on to a sharply conicalheaded screw45c for the highest-note string pair. By this arrangement there isprovided in a particularly convenient manner, and with preservation ofready electrode adjustability, an angling of the electrode surfaces withrespect to initial string vibration plane which is known as desirablefor the reduction of undue initial nonmusical raphtransientsaccompanying the excitation of the higher frequency notes.

Figure 7, because of its appropriately large scale, has been selectedalso to show a purely electrical means for reducing these -rap effects.This comprises filter means at least partially interposed in theconnections between the highnote electrodes 45c-- l5b45a and thelower-note electrodes 45, and effective-preferably in degree increasingwith frequencyto eliminate from the outputs of the high-note electrodesa band of lower frequency components of which the rap is largelycomposed. Filter means so disposed may take a variety of forms, but theone I have chosen for illustrative purposes may comprise a shuntcircuit, from the highest-note electrode 450 to ground, of inductance55, capacity 56 resonant with the inductance to the mean rap componentfrequency, and resistance 5'! adjustable to control the circuit; andseries elements comprising resistances 58 connecting the successivehighnote electrodes together and to the lower-note.

electrodes 45. It will be clear that as to electrode 450 there isprovided the maximum shunting to ground of the rap components, and amaximum of series impedance to the conductor 46 and amplifier input; andthat both these characteristics are progressively decreased forelectrodes associated with progressively lower notes.

The vibratile system which supports and couples the strings may bereferred to as the resonator portion of the instrument, in that it ischiefly responsible for the direct acoustic sound output of theinstrument. In the particularly illustrated instrument this portion hasbeen made relatively restricted and skeleton-like, by the omissiontherefrom of a continuous soundboard; accordingly the rate of damping orgeneral decadence of the tones of the instrument is normally appreciablyless than that of the conventional piano, and in many instances it maybe desirable to increase this damping rate. In the instrument accordingto the invention the damping rate may be increased by a damping meansassociated with the strings, preferably uniformly along their activeportions so that their vibrations are not otherwise interfered with.Such a damping means may comprise a thin coating, about at least thoseactive string portions, of elastic material characterized by at leastsome internal friction; a lacquer or rubber compound may for example beemployed. Some-still further damping increase, due probably more to anincrease of air-resistance than of internal friction, may be secured byblowing onto the lacquer or other compound, while wet, felt dust orother finely divided and relatively soft and sound-absorbent particles;upon drying of the coating the outer portions of these particles willremain exposed to the air. Such a coating on the strings has beenfractionally indicated as 60 in Figure 3, but in greatly exaggeratedthickness for the sake of clear illustration.

A similar coating with the felt or like dust, or other covering of feltor other sound absorptive material, may be applied directly to theresonator portion, whether that is or is not' restricted as in theparticularly illustrated instrument. Thus there has been fractionallyillusu-ated as ii in Figure 3 such a coating on both the front and backsurfaces of the ribs 8, and as 62 such a coating on the backs of thebridges 4| and 43. Such a covering of the resonator portion not onlyincreases the air-damping of that portion and hence the tone-dampingrate, but also decreases the direct sound output of that system andhence of the instrument, and furthermore very beneflcially reducesacoustic feed-back of sound from the loudspeaker to the strings. Thisdirect application of sound-absorbent material to the resonator portionof an instrument I have found to be a much simpler procedure than theabsorption of sound which that portion has once been permitted tocreate.

The apparent damping of the tones of the instrument is always greaterfor high string-excitation strengths than for low ones, since the rateof damping appears to vary with string vibration amplitude; ordinarily,however, the distinction in damping rate so produced tends to beobscured by the accompanying large change in output volume. According tomy invention I may effect an improved control over apparent damping rateby simultaneously controlling both the excitation strength and theefficiency of the mechanico electro-acoustic translation (e. g., thegain of the amplifier 3436-38)and I may do this while maintainingsubstantia ly constant volume level, by controlling that strength andthat efliciency in appropriately predetermined inverse relationship.This I have illustrated in Figure 6 by employing, for example as thecontrol means 31 above mentioned, a potentiometer 64 connected acrossthe output of amplifier portion 36, and having a variable contact 65mechanicaly connected with the rod 25b abovementioned as controlling thehammer-stroke in response to pedal 25--the input of the amplifierportion 38 being connected to one extremity of the potentiometer and tothe variable contact 65. Ordinarily operation of the pedal 25 will notonly decrease the hammerstroke but will also increase the translationefficiency by raising the contact 65, the potentiometer 64 beingsuitably tapered so that the effects of these two operations on output,volume substantially annul each other; the apparent damping rate willbe decreased, however, during the pedal depression. If desired, thisaction may be eliminated at will to leave the pedal 25 as a simplehammer-stroke control, by employing a switch 56 to break the connectionof amplifier portion 38 to the movable contact 65 and instead to connectit to a fixed tap 61 appropriately positioned on the potentiometer 64.

For simple volume control purposes I incorporate, in the preferredinstrument according to my invention, a pair of volume control meansonebeing a full-range control manipulable by hand to establish the generalvolume level; and the other being connected to an upwardly biased pedal,such as 10 in Figure 1 and the cross-sectional Figure 8, to temporarilyreduce the volume within finite limits during periods of pedaldepression. The former may be connected in the control means 351), andthe latter may'be connected as the control means 351: abovemen tioned.Thus in 35!) (see Figure 8) there may be included, as thehand-manipulable control, a potentiometer ll connected across the outputof amplifier portion 34, and having variable contact 12 and oneextremity connected to the input of amplifier portion 36; while thepedalresponsive volume control may comprise a plurality of resistances13 progressively shuntable I sealing 'means across the potentiometer Ilasthe pedal 10 is depressed. This pedal, which may be both eflectivelyterminally pivoted and upwardly biased by spring 69', may be disposedabove a plurality of normally spacedcontacts 14, 14a, 14b and 140;contact 14 may be'conn'ected to one extremity of thepotentiometer II,and the other contacts to the other extremity of the potentiometerthrough respective resistances 13. As the pedal 10 is depressed it willfirst close contact- I4 against contact 14a, shunting one of theresistances 13 across the potentiometer and slightly reducing thevolume; and as the pedal is further depressed, more and more of thecontacts will be closed, to shuntmore and more of the resistances acrossthe potentiometer and to more and more reduce the volume. The limit ofvolume reduction, however, is deliberately made a-finite one forcorrespondence with normal piano soft pedal action.

If desired, the pedal-l8 may be made to function as a normal soft, orhammer-stroke-reducing, pedal coincidentally with its function as anelectrical volume control pedal. This has been illustrated in. Figures 1and 8 by the extension of the lever 25a to above the pedal 18, the freepassage through the lever extremity of a rod 10a extending upwardly fromthe pedal, and the threading of a removable nut 10b onto the top of therod 10a to a position just above the lever 2511. With the nut in place,depression of pedal 10 will rock lever 250. (about its pivoting spring250, Figure 1) to reduce the hammerstroke simultaneously with theoperation of the contacts 14, etc; but a like rocking of the lever 25aby the pedal 25 will neither move the pedal 10 nor operate thosecontacts, in view of the free passage of rod 18a through lever 25a. Thesimultaneous electrical and mechanical control of tone volume, withattendant influences of the mechanical control on other tonecharacteristics, has proven highly pleasing musically. t

The control means 35b may typically include,

ture or tone control means operating on an absolute frequency basis.These have been illustrated as a condenser 15 and variable resistanceIS, in series with each other and together shunted across the output ofpotentiometer H, serving as a high-frequency control; and a condenser 11and variable resistance I8, 11 being in series and 18 in shunt with theinput of amplifier portion 36, serving as a low-frequency control. Itwill be understood, however, that the form and location 01' thesecontrols have been chosen only by way of example and in no sense aslimitative. The entire control means 35b may be physically arranged in asmall panel assembly at the right of the instrument just above the keys28, as has been indicated in Figure 1; this panel assembly may alsoinclude an on-off switch 19 for the amplifier 34--3838.

The charging resistance 3|, input condenser 32 and input resistance 33are desirably encased within a grounded electrostatic shieldingenclosure 38 as indicated schematically in Figure 3. To preventvibration within, and consequent variation bf their capacity to, theenclosure 80, and simultaneously to .protect them against moisture andconsequent leakage, I have found it advantageous to surround them withinthe enclosure by (fractionally shown as 80a) poured hot into theenclosure and imbedding ,thes elements therein when 0001. The shield-'ing provided by the enclosure 88 may advanin addition to potentiometerII, harmonic struc tageously be extended about the input and outputleads therefor, as indicated by 8| in Figure 3.

Electrostatic shielding of further sensitive instrument portions,especially the electrodes, is basically provided on the front by thestrings; to complete it on the rear there may be provided a removableback cover for the instrument, fractionally shown in withdrawn positionas 82 in Figure 8. This may comprise a rectangular frame work 83 havinghorizontal cross-pieces such as 84 and vertical cross-pieces such as 8!,and grounded metallic screening 86 secured across the frame-work andcross-pieces and trimmed by moulding ,8] if desired. Preferably eachindividual element of the framework and cross-pieces will be providedwith a coating of colloidal graphite solution which dries in aconductive state, as has been fractionally illustrated by the heavylines 88 in Figure 3, and the coatings of the several elementsindividually electrically grounded.

With the back cover secured against the rear of the instrument thegrounded screening 86 is disposed relatively near the electrodes 45; and

it is to minimize shaking of this screening, which wouldelectrostatically influence the electrodes, that the cross-pieces 84 and85 are employed.

To supplement this basic shielding the inside surfaces of theinstrument, comprising for example those surfaces of the end standards3, floor member Illa, and removable front cover member II, may beprovided with similar grounded coatings. This has been illustrated indetail for the front cover member II in a back. view thereof appearingas Figure 9. This has been shown as formed of the several mutuallysecured boards Ha, Hb, .Ilo, lid, the whole exposed surfaces of all theboards being provided with respective coatings fractionally shown as 89.A convenient means of individually ground ing the coatings of individualelements has been illustrated for the several boards of which member IIis formed; this may comprise a metallic conductor 90 successivelyconnected as by screws 9| to one or more places on each element, theconductor being fully or substantially grounded, at one place forexample, in any convenient manner. This expedient obviates excessiveresistance in the shielding, both as resulting from large area coveredby the coatings and as resulting from possibly poor continuity of thecoatings between successive elements.

The low-frequency and high-frequency loudspeakers, 39 and respectively,are mounted within the instrument in a preferred embodiment of theinvention, and they have been so illustrated. The low-frequency speakermay be supported to the plate I as by securing to a cross member 93extending between one of the web-flanges 4 and the edge flange 2 abovementioned. It may be forwardly directed, and baiiled, if desired, by theremovable front cover member ii when in its installed positionthismember having been illustrated as provided with the appropriatesound-emitting aperture H. The relatively smaller high-frequencyloudspeaker 48 may be secured to the plate I in any convenient manner,likewise preferably fcrwardly directed, and the front cover member ay beprovided with the second soundin any convenient manner,

emitting perture ll" appropriate to it. A pre-,'

the high-frequency speaker relatively adjacent the high-note extremity,of the keyboard and instrument, and the speakers have been accordinglyso illustrated. I have found this arrangement markedly to enhance thenaturalness of pianistic performance by an instrument of this type. Noclaim, however, is made to this arrangement of speakers in thisparticular application.

In the instrument so described it will be appreciated that there is asubstantial acoustic-vibrational influence exerted by the loudspeaker onthe strings; the very close adjacency of the loudspeaker to therestricted resonator portion (which is vibrationally coupled with thestrings) causes this influence to be of the same order as would amoderate adjacency of the loudspeaker to a more complete resonator (e.g., soundboard). In

any instrument wherein this substantial influence or feed-back to thestrings is present I have found that the securing of themechanico-electric translating (i. e., electrode) means to the resonatorportion (i. e., vibratile system) has the peculiar and highly beneficialfunction of markedly suppressing the effect of that feed-back i. e., aregenerative or self-oscillatory tendency of the system, which would beof a prohibitive order were the translating means secured to relativelyrigid portions such as the plate I. In such an instrument as thatdisclosed in U. S. Patent No. 1,912,293 to me, above mentioned, the likesecuring of the translating means-while otherwise beneficial-did notperform this additional function, in view of the substantial absence offeed-back, resulting from joint restriction of the resonator portion andcomparative isolation therefrom of the loudspeaker. The beneficialfunction above described is performed in the currently describedinstrument by reason of the participation of the translating means (orat least the sensitive portions thereof) in the appreciable compositevibration of the resonator portion and strings which is produced by thecompressional waves from the loudspeaker-so that in spite of appreciablevibrational amplitude the sensitive spacings between (or relativepositions of) the translating means and the strings tend to remainconstant.

It is of course true that the resonator portion vibration may stimulateindividual strings into small individual vibrations of their own, sothat those strings to that extent depart from the composite vibration ofresonator portion, strings and translating means; these individualstring vibrations can of course influence the translating means. Whilewithout special attention to this phenomenon a large suppression of thefeed-back effect is obtained as outlined in the preceding paragraph,this effect "is even more perfectly suppressed by proper furtherarrangement of the translating means in such positions longitudinally ofthe strings that they do not have a strong response to thesefeed-back-produced individual string vibrations. Ordinarily I find thesevibrations to be predominantly at relatively high-numbered partialcomponents of the strings, so that their amplitude is as great veryclose to the string end as it is nearer the string center; for efficientintended translation, however, the spacing of the translating means fromthe mean string position tends to be greater, and the influence of ahigh-numbered partial component vibration therefore less, the furtherthat means is from the string end. Accordingly the desirablelongitudinal position for the translating means is at an appreciabledistance from the string end; and the cured as to vibrational jointobservance of this specification and that of securing the translatingmeans to the resonator portion, in an instrument with appreciableloudspeaker-to-strings feed-back, insures a surprising absence of effectof the feed-back-i. e., of regenerative and self-oscillatory tendencies.

While I have disclosed my invention in terms of a preferred embodimentthereof, it will be understood that no unnecessary limitations areintended by virtueof the details of that embodiment; for modifications,many of them wide, which will suggest themselves to those skilled in theart may fall within the true spirit and scope of the invention. In manyof the claims hereunto appended I undertake to express that scopebroadly, subject however to such proper limitations as the state of theart may impose.

I claim:

1. In an electronic piano having vibratable strings: a bridge to whichsaid strings are semovement; vibratile means supporting said bridge forboth linear and rocking response of said bridge to string vibrations;and pick-up electrode means passing through and supported by the samebridge and extending into spaced relationship to said strings.

strings a bridge to which said strings are secured as to vibrationalmovement; vibratile means supporting said bridge for both linear androcking response of said bridge to string vibrations; a portion integralwith and extending from said bridge under said strings; and pick-upelectrode means passing through and supported by said portion andextending into spaced relationship to said strings.

4. In an electronic piano having vibratable strings: a bridge contactedby and supporting said strings; and pick-up electrode means carried bythe same bridge, the surface of said bridge between said electrode meansand the region of contact of said strings therewith being slotted to asubstantial depth.

5. In an electronic piano having vibratable strings: a bridge contactedby and supporting said strings; and pick-up electrode means carried bythe same bridge, said bridge being of wood but containing in at least asurface layer portion a substantial percentage of oil.

6. In an electronic piano having vibratable strings and a plurality ofvibratile ribs; stringbridge means secured to said ribs and having saidstrings secured thereto as to vibrational movement; and adjacent bridgemeans and pickup electrode means carried thereby. at least saidstring-bridge means extending about and being secured to three surfacesof each of said ribs.

"7. In an electronic piano having vibratable strings: string-bridgemeans contacted by and supporting said strings; adjacent bridge means;

a common vibratile support for both said bridge tive second ends formedfor tool manipulation whereby to adjust said spaced relationship.

8. In an electronic piano including a pair of adjacent, substantiallyparallel and similarly tuned strings: a pick-up electrode screw for saidstrings, the axis of said screw being substantially centered between,and substantially normal to the plane of, said strings; and a conicalhead on said screw adjacent said strings.

9. In an electronic piano having a series, of

pairs of vibratable strings tuned to progressive frequencies: pick-upmeans for said strings comprising a plurality of electrode screws havingconical heads respectively substantially centered with respect to saidpairs of strings, the apex angles of said conical heads beingprogressively more acute toward the treble extremity of said stringseries.

10. In an electronic piano having a plurality of strings tuned toprogressive frequencies: means for translating electric oscillationsfrom the vibrations of said strings, including pick-up electrodesrespectively associated with said strings and electrical connectionsbetween said electrodes; and filter means, at least partially interposedin saidconnections, for progressively attenuating predeterminedcomponents in the oscillations translated from progressively moreextreme-frequency strings.

11. In an electronic piano having a plurality of impulse-excitablestrings tuned to progressive frequencies: means for translating electricoscillations from the vibrations of said strings, including pick-upelectrodes respectively associated with said strings and electricalconnections between said electrodes; and filter means, at leastpartiallyinterposed in said connections, for progressively attenuatingpredetermined transient components in the oscillations translated fromprogressively higher-frequency strings.

12. In an electronic piano having a plurality of vibratable stringstuned to progressive frequencies, and an amplifier: means fortranslating electric oscillations from the vibrations of said strings,including pick-up electrodes respectively associated with said strings,electrical con nections between said electrodes, and means connectingsaid electrodes to the input of said amplifier; resistances seriallyinterposed in said connections; and a frequency-discriminating shuntcircuit connected to an electrode remote from said amplifier-connectingmeans.

13. In an electronic piano including mechanico-electro-acoustictranslating means having a negligible damping reaction: a vibratablestring influencing said translating means; and a. thin coating ofdamping material surrounding said string whereby an appreciable dampingreaction of said translating means is simulated.

14. In an electronic piano including mechanico-electro-acoustictranslating means having a negligible damping reaction: a vibratablestring influencing said translating means; and a thin coating,surrounding said string, of elastic material characterized by at leastsome internal trio-- I tion, whereby an appreciable damping reaction"said string, whereby an appreciable damping reaction of saidtranslating means is simulated.

16. In an electronic piano including vibratable strings andmechanico-electro-acoustic translating apparatus influenced by buthaving a negligible damping reaction on said strings: a vibratilestructure supporting and vibrationally coupled with said strings; andsound-absorptive material secured on at least portions of the surface ofsaid structure, whereby an appreciable damping reaction of saidtranslating means on said strings is simulated.

17. In an electronic piano including vibratable strings and means fortranslating electric scillations from their vibrations: a vibratilestructure supporting and vibrationally coupled with said strings; anelectro-acoustic translating device responsive to said oscillations andexerting asubstanti'al vibrational influence on said vibratilestructure; and sound-absorptive material secured to at leastmortions ofthe surface of said structure, whereby said vibrational influence issubstantially reduced.

18. In an electronic piano including vibratable strings, means forefiecting impulse excitation thereof, and mechanico-electro-acoustictranslating means responsive to said strings: means for varying thestrength of said excitation, and means, connected and operatedconcomitantly with said strength-varying means, for varying theefficiency of said translating means.

19. In'musical tone production from a damped tuned vibrator, the methodof control of apparent tone damping rate whichcomprises effecting animpulse excitation of-the vibrator, efiecting amechamco-electro-aco'ustic translation from the resulting vibrations ofthe vibrator, and controlling the strength of said excitation and theefiiciency of said translation in inverse relationship to each other.

20. In an electronic piano including vibratable strings andmechanico-electro-acoustic translating means responsive thereto: aterminally pivoted and upwardly biased pedal; and volume-control means,electrically connected with said translating means, mechanicallyconnected with said pedal, and operated by depression of said pedal tofinitely reduce the efliciency of said translating means.

21. In an electronic piano including vibratable strings andmechanico-electro-acoustic translating means responsive thereto: aterminally pivoted and upwardly biased pedal; a plurality ofresistances; a plurality of contact means respectively connected withsaid resistances, and progressively responsive to depression of saidpedal to progressively shunt said resistances across an electricalportion of said translating means.

22. In an electronic piano including vibratable strings, hammers movableto excite said strings, and mechanico-electro-acoustic t r a n s l'a tin3 means responsive to said strings: a pedal; means connected with andoperated by the pedal for reducing the range of movement of saidhammers; and volume-control means, electrically connected with saidtranslating means, mechanically connected with said pedal, and operatedby operation of said pedal to finitely reduce the emeiency of saidtranslation.

23. In an electronic pianoincluding vibratable strings, pickup electrodemeans in spaced rela tion thereto "nd forming a capacity therewith,means for c arging said capacity, and an electronic amplifier: an inputresistance and an input condenser for said amplifier; a resistance forsaid charging means; an electrostatic shielding enclosure for saidresistances and condenser; and sealing means surroundingsaid resistances-sociated therewith: means for shielding said sensitive portionscomprising a substantially nonconductive member; a coating ofappreciably conductive material carried by the surface of said member;and a metallic conductor interconnecting a plurality of intermediateportions of said coating.

25. In an electronic piano including vibratable tuned strings and anamplifier for string-vibration-representing oscillations: a vibratilesystem supporting and vibrationally coupled to said strings; anelectro-acoustic translating device fed by said amplifier and exerting asubstantial vibrational influence on said strings through said vibratilesystem; and mechanico-electric translating means feeding said amplifier,and having sensitive portions in spaced relationship to and responsiveto said strings and carried by said vibratile system for vibrationalinfluence by said electro-acoustic translating device jointly with saidstrings.

26. In an electronic piano including vibratable tuned strings and anamplifier for string-vibration-representing oscillations: a vibratilesystem supporting and vibrationally coupled to said strings; anelectro-acoustic translating device fed by said amplifier and exertingthrough said vibratile system a composite vibrational influence on saidstrings and individual vibrational influences on the several strings;and mechanico-electric translating apparatus feeding said amplifier, andhaving sensitive portions in spaced relationship to and responsive tosaid strings and carried by said vibratile system for vibrationalinfluence by said electro-acoustic translating device correspending withsaid composite string vibrational influence, said sensitive portionsbeing so positioned longitudinally of said strings that they aresubstantially unresponsive to said individual string vibrationalinfluences.

27. In a musical instrument including a vibrator and means fortranslating sound from the vibration thereof: the combination of anexciting system for said vibrator, including means for effectingexcitation of said vibrator at different strengths; and means,controlled by said exciting system and inversely responsive to thestrength of said excitation, for varying the efiiciency of saidtranslating means.

BENJAMIN F. MIESSNER.

